The present invention relates to a lower vehicle-body structure of an automotive vehicle which comprises a tunnel portion provided at a central portion, in a vehicle width direction, of a floor panel and extending in a vehicle longitudinal direction, right-and-left side sills provided at right-and-left both-side portions of the floor panel and extending in the vehicle longitudinal direction, and right-and-left intermediate pillars extending in a vehicle vertical direction from the right-and-left side sills.
In general, a lower vehicle-body structure of an automotive vehicle uses a seat-rail support structure in which a cross member extending in the vehicle width direction is provided between a portion of a side sill which is positioned near a center pillar and a tunnel portion, another cross member is provided in front of the above-described cross member, and a seat rail is supported at the front-and-rear both cross members.
The two cross members are necessary in the above-described structure. Accordingly, another lower vehicle-body structure has been proposed in order to reduce a vehicle weight, in which a single cross member extending in the vehicle width direction is provided between a portion of the side sill which is positioned near the center pillar and the tunnel portion, a seat-rail mounting seat is provided at a floor panel or the tunnel portion, and the seat rail is attached to the cross member and the seat-rail mounting seat and supported at these members.
The above-described conventional structure can reduce the vehicle weight by using the single cross member, not two members. However, since a range where the tunnel portion is not supported at any frame structural body becomes larger, this conventional structure has a problem that a mouth opening deformation of a front-side portion of the single tunnel portion positioned in front of the cross member and a rear-side portion of the tunnel portion positioned in back of the single cross member is improperly enlarged, so that noises may be caused and thereby quietness in a cabin may deteriorate.
Herein, it may be considered that a bracket for forming the seat-rail mounting seat is so prolonged in the vehicle longitudinal direction that move of the tunnel portion can be suppressed by this bracket. However, this long bracket may cause an weight increase improperly despite the above-described weight reduction attained by using the single cross member. Therefore, there is still room for improvement.
Meanwhile, Japanese Patent Laid-Open Publication No. 2013-103528 discloses a structure in which a front portion of a seat rail is attached to and supported at a cross member which is provided between a side sill and a tunnel portion, and a rear portion of the seat rail is attached to and supported at a seat-rail mounting seat which is provided at the tunnel portion.
This structure of the patent document has a problem that the mouth opening deformation of the tunnel portion at a position which corresponds to a lower portion of a center pillar becomes so larger, compared to the conventional structure using the two cross members, that the noise performance may deteriorate.
The inventors of the present invention conducted some experiments repeatedly and finally found that in a case in which the single cross member is used, the tunnel portion moves around this cross member such that its front and rear portions move in a reverse phase. Consequently, the inventors made the present invention by focusing on this reverse-phase move of the tunnel portion.